1. Field of the Invention
This invention relates to a liquid jet recording apparatus for discharging droplets of recording liquid and causing them to adhere to a recording medium such as paper to thereby accomplish recording of various kinds of information.
This invention also relates to a liquid jet recording apparatus particularly suitable for a line type recording head in which the dot slip from an orifice suffering from improper discharge can be corrected.
2. Related Background Art
In a liquid jet recording apparatus, droplets of ink (recording liquid) are discharged from discharge openings provided in a recording head and the discharged droplets are caused to adhere to a recording medium such as paper to thereby accomplish recording and therefore, there are many advantages that the rate of occurrence of noise is very small, that high-speed recording is possible and that plain paper can be used and recording paper of special characteristic is not required, and recording heads and liquid jet recording systems of various types have heretofore been proposed.
Also, liquid jet recording apparatuses in which recording liquid is discharged from a recording head to a recording medium such as paper or a plastic sheet and recording of characters, images, etc. is effected by a dot matrix suffer less from noise during the operation than the other recording apparatuses, and further has an advantage that the mechanical structure thereof is basically simple and inexpensive, and are adopted in various fields as the recording output apparatuses of computers, word processors, etc.
In such liquid jet recording apparatuses, recording is generally effected while a recording medium is conveyed intermittently or continuously in one direction.
Also, in recent years, as an improvement in recording speed gradually becomes required, there have come to be proposed many apparatuses having a line type recording head in which a number of recording liquid discharge openings corresponding to the full width of a recording medium are arranged in the form of a line.
Above all, a recording head of the type in which heat energy is caused to act on ink to thereby discharge the ink from the discharge openings has advantages such as good responsiveness to a recording signal and ease of the highly dense multiplication of discharge openings (see U.S. Pat. Nos. 4,723,129 and 4,740,796).
A typical example of the construction of the recording head of such a type which utilizes heat energy as ink discharge energy is shown in FIGS. 1A and 1B of the accompanying drawings. FIG. 1 shows a schematic cross-section of the recording head in the direction of a flow path, and FIG. 1B shows the relation between the joined positions of a base plate and a top plate. Also, FIG. 1B shows portions of the recording head in a schematic perspective view.
This recording head is of a construction in which electro-thermal converting members are arranged on a base body 18 and a top plate 12 is joined to a head base plate 18' in which a protective layer 11 is provided on heat generating resistors 15 and electrodes 10 in the electro-thermal converting members which are finally located below a flow path 13 and a liquid chamber 17, whereby the flow path 13 and the liquid chamber 17 are formed. In the case of the recording head shown, discharge openings 14 are formed by the head base plate and the top plate 12 being joined together.
The ink discharge energy in this recording head is imparted by an electro-thermal converting element having a pair of electrodes 10 and a heat generating resistor 15 located between these electrodes. That is, when an electric current is applied to the electrodes 10 to thereby cause the heat generating resistor 15 to generate heat, the ink in the flow path 13 lying near the heat generating resistor 15 is momentarily heated to create a bubble there, and a droplet of the ink is discharged from the discharge opening by a change in volume caused by the momentary expansion and contraction of the volume which in turn is caused by the creation of the bubble.
In a liquid jet recording apparatus using such a recording head (referred to also as an ink jet printer), the clogging of the discharge openings provided in the recording head and the entry of a bubble into an ink supply path communicating with the discharge openings may cause the deterioration of the liquid droplet discharging performance and accordingly improper ink discharge.
So, in the liquid jet recording apparatuses according to the prior art, suction means capable of opposing these discharge openings has been provided outside the discharge openings to thereby suck the ink out of the discharge openings, or the ink in the ink supply path has been pressurized to thereby cause the ink to flow at a certain degree of speed and discharge the ink from the discharge openings, whereby the causes of the improper ink discharge as noted above have been eliminated.
Where recovery is impossible by the recovery operation from the improper discharge described above, for example, in the case of trouble caused by the disconnection or the like of the heat generating resistors, the recording head has been manually interchanged.
However, in the liquid jet recording apparatus as described above, the recoverable improper ink discharge resulting from the dust near the discharge openings or the entry of a bubble into the ink supply path leading to the discharge openings and the unrecoverable improper ink discharge resulting from the trouble of the electrical system such as the disconnection or deterioration of the heat generating resistors or the short-circuiting or disconnection of the electrodes could not be judged or distinguished from each other. Therefore, in the prior-art apparatus, whenever improper ink discharge has occurred, it has been the practice to perform the recovery operation for recovering from the improper discharge by sucking the ink out of the discharge openings or pressurizing the interior of the ink supply path.
Accordingly, heretofore, even in the case of the unrecoverable electrical trouble such as the disconnection of the heat generating resistors as noted above, the above-described recovery operation has been executed several times to thereby waste the ink and time.
To solve such a problem, there is known from Japanese Laid-Open Patent Application No. 62-152887 a detecting device for detecting any abnormality when due to the electrical disconnection or the like of the recording head, the recording head is not driven by the driving means therefor. Again in this case, however, in a liquid jet recording apparatus shown in the schematic perspective view of FIG. 2 of the accompanying drawings, when the user judges the trouble to be an unrecoverable trouble, the user himself must remove the recording head 22 and replace it with a new recording head, and this has led to the problem that the recording apparatus becomes unusable until the replacement of the recording head.
Also, the aforedescribed line type recording head has a huge number of discharge openings and therefore, the probability with which discharge openings of improper discharge in which the discharge of recording liquid will become impossible due to the disconnection or contamination of the head in spite of the so-called recovery operation being performed while the head is repetitively used come into existence becomes higher. If discharge openings of such improper discharge come into existence, there will arise the problem that there can be obtained only recorded images of low quality having so-called dot slips.
To improve the quality of recording, the recording head in which the discharge openings of improper discharge have come into existence can be replaced with a new head, but the line type recording head, which has a huge number of discharge openings, is expensive as compared with ordinary recording heads and the cost of replacement becomes remarkably high.